Second...exactly. From the BG's perspective, the threat was not stopped until he could return (accurately even) fire. It's not about what eventually kills the BG, it's about stopping the threat in the most expeditious manner.

The .38, with the loads of the day, were lacking as well.

That is exactly right. The fact that the bad guy will eventually die is no consolation to my family. Some guys have a lot of fight in them even with wounds that would eventually prove fatal (Miami FBI shoot out comes to mind).

People keep mentioning how birdshot is not lethal through walls. What happens if the bad guy does something crazy like use a wall as cover. If he has a hangun, and you are loaded with birdshot he is behind cover, and you are behind concealment.